One-Paragraph Summary
Palo Alto Networks Unit 42's report,
"Pass the Passkey: A Novel Attack Surface in Passwordless Authentication," exposes how malware running on a compromised endpoint can exploit onboarding, recovery, and device-trust workflows in Google Cloud Authenticator to execute full account takeovers of passkey-protected accounts. By demonstrating three distinct attack vectors collectively named
"Pass-ta-key", the researchers show that unprivileged endpoint malware can bypass user consent, user verification (such as biometrics/PINs), and hardware-backed TPM protections to forge assertions, trick cloud authenticators, or exfiltrate plaintext passkey private keys. These findings reveal that while passkeys effectively eliminate traditional password phishing and credential-dumping attacks, they shift the threat model toward endpoint security and cloud authenticator implementation risks.
Key Takeaways & Important Details
1. Stage Zero Reconnaissance (Local Data Harvesting)
- Unprivileged Access: Chrome stores synced passkey records locally within %LocalAppData%\Google\Chrome\User Data\<Profile>\Sync Data\LevelDB as proto-encoded WebauthnCredentialSpecifics records.
- Target Identification: Without requiring elevated administrator privileges, local malware can enumerate targeted accounts, usernames, credential IDs, and encrypted private key structures before launching an attack.
2. The Three "Pass-ta-key" Attack Classes
- Pass-ta-key Attack (Device Identity Impersonation):
- Mechanism: Chrome stores its TPM-wrapped identity private key (wrapped_identity_private_key) inside passkey_enclave_state. Malware reads this blob and uses standard Windows Cryptography API (CNG) calls (NCryptSignHash) to issue signing requests to the TPM without triggering device-unlock prompts or administrative elevation.
- Impact: The malware initiates a WebSocket session with Google Cloud Authenticator, obtains valid signed assertions from the cloud enclave, and logs in as the victim without biometrics, PINs, or user interaction.
- Silver Pass-ta-key Attack (Bypassing User Verification / Biometrics):
- Mechanism: Exploits weaknesses in how device trust and user verification (UV) state are asserted to the cloud authenticator.
- Impact: The attacker deceives the cloud authenticator into believing that biometric or PIN verification succeeded on the client. Once the initial token is obtained, the attacker can complete the account takeover remotely from their own machine without needing ongoing access to the victim's physical device.
- Golden Pass-ta-key Attack (Exfiltrating Synced Private Keys):
- Mechanism: Misuses device onboarding and key recovery workflows within the cloud authenticator architecture.
- Impact: Allows the attacker to extract raw, synced passkey private keys in plaintext. Once exfiltrated, these keys can be copied, exported, or traded on cybercrime marketplaces, completely undermining the "non-transferable" premise of passkey credentials.
3. Defensive & Security Implications
- Shift in the Threat Surface: Passkeys eliminate server-side database leaks and phishing, but they move the battleground to client endpoints and identity sync architectures.
- TPM & Software Limits: Hardware-backed protections (like TPMs) only protect keys from raw extraction if software API layer restrictions or user-presence enforcement are improperly designed.
- Mitigation Focus: Security teams must prioritize endpoint detection and response (EDR/MDR), identity security controls, and strict privilege management to detect local key usage anomalies before malware can hijack cloud authenticator workflows.
) or for convenience. For example, on MT, whenever I got logged out unexpectedly—or used to have to supply the TOTP code monthly—I now use a fingerprint reader to authenticate. That’s convenient; it’s hard to go back.
